I guess that's because Google largely won the "container wars", being the first to market with a reasonably complete feature set, brand reputation and resources for continued development, offerings by most cloud vendors and also a large dose of hype in the form of developer talks, demos, press releases/newsletters, tutorials, learning resources and i guess even certifications. Of course, that wasn't all just Google - once the hype around it started, numerous parties joined in, wanting recognition, relevant skills, or even to market their products that are built around supporting the complexity of Kubernetes.

Compare that to something like Apache Mesos, which, while initially promising, largely fell by the wayside and never really caught on: https://mesos.apache.org/

Larger surface area that can be controlled programmatically without needing to involve the people managing the hardware or network. This makes certain engineering choices (like microservices) more tenable.